Tires for vehicles such as automobiles, motorcycles, scooters, bicycles and wheelchairs are divided into two types: tubed and tubeless tires. The tubed tires include an outer rubber shell and an inner rubber tube mounted therein. The tubeless tires have recently been put into practice. The expansive force of air filled in the tires renders the tires cushiony irrespective of the tire type. However, the tires may be punctured by sharp objects such as nails or pieces of glass during use or may lose air pressure when injection valves fail. Further, air permeability of the rubber tubes causes air leakage through gaps between the rubber molecules, inevitably resulting in a drop in air pressure.
In order to solve such shortcomings, new tires have been developed and are currently in use, for example, solid tires composed wholly of a lump of rubber, urethane foam tires made of polyurethane foams, and foam filled tires filled with foams, such as urethane foams, instead of tubes. However, these new tires have the inherent defects despite their advantages. Specifically, the solid tires are robust and protected from going flat but are excessively heavy and cushionless. The urethane foam tires are lightweight but lack elasticity. Other drawbacks of the urethane foam tires are that they are hydrolysable, resulting in poor durability, and undergo rapid surface oxidation when exposed to sunlight. The foam filled tires are heavy, insufficiently elastic, and expensive.
On the other hand, ethylene copolymers foams such as ethylene vinyl acetate (EVA) foams are used in tires for baby carriages and tires for children's bicycles. However, such tires have low grip forces, slippery surfaces, and poor braking performance, limiting their applications to vehicles designed to move slowly and carry low loads, such as baby carriages and children's bicycles. Ethylene copolymers are susceptible to softening at high temperature, particularly, in the summer season, resulting in a reduction in hardness. If an obese person rides a baby carriage or children's bicycle, the tires shake, and as a result, an accident tends to happen. The temperature of asphalt roads rises to about 65° C. at an ambient temperature of about 30° C. The friction between tires and the ground further increases the road temperature to 70-80° C.